1. Field of the Invention
Embodiments disclosed herein relate generally to carbide composite materials. In particular, embodiments disclosed herein relate to carbide composite materials for use in hardfacing materials or other cutting tool components.
2. Background Art
In drilling oil and gas wells or mineral mines, earth-boring drill bits are commonly used. Typically, an earth-boring drill bit is mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface. With weight applied to the drill string, the rotating drill bit engages an earthen formation and proceeds to form a borehole along a predetermined path toward a target zone.
Historically, there have been two types of drill bits used drilling earth formations, drag bits and roller cone bits. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled. Several types of roller cone drill bits are available for drilling wellbores through earth formations, including insert bits (e.g. tungsten carbide insert bit, TCI) and “milled tooth” bits. The bit bodies and roller cones of roller cone bits are conventionally made of steel. In a milled tooth bit, the cutting elements or teeth are steel and conventionally integrally formed with the cone. In an insert or TCI bit, the cutting elements or inserts are conventionally formed from tungsten carbide, and may optionally include a diamond enhanced tip thereon.
The term “drag bits” refers to those rotary drill bits with no moving elements. Drag bits are often used to drill a variety of rock formations. Drag bits include those having cutting elements or cutters attached to the bit body, which may be a steel bit body or a matrix bit body formed from a matrix material such as tungsten carbide surrounded by a binder material. The cutters may be formed having a substrate or support stud made of carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface.
Typically, a hardfacing material is applied, such as by arc or gas welding, to the exterior surface of the steel components (e.g., milled teeth or steel bit body) to improve the wear resistance of the area of the bit (or other downhole tools needing body protection). The hardfacing material typically includes one or more metal carbides, which are bonded to the steel components by a metal alloy (“binder alloy”). In effect, the carbide particles are suspended in a matrix of metal forming a layer on the surface of the steel. The carbide particles give the hardfacing material hardness and wear resistance, while the matrix metal provides fracture toughness to the hardfacing.
Many factors affect the durability of a hardfacing composite or other carbide component such as cutting elements in a particular application. These factors include the chemical composition and physical structure (size and shape) of the carbides, the chemical composition and microstructure of the matrix metal or alloy, and the relative proportions of the carbide materials to one another and to the matrix metal or alloy. The metal carbide most commonly used in hardfacing and cutting elements is tungsten carbide. Small amounts of tantalum carbide and titanium carbide may also be present in such material, although these other carbides may be considered to be deleterious.
Many different types of tungsten carbides are known based on their different chemical compositions and physical structure. The types of tungsten carbide commonly typically used in hardfacing and cutting elements are cast tungsten carbide, macro-crystalline tungsten carbide, carburized tungsten carbide, and cemented tungsten carbide (also known as sintered tungsten carbide).
Tungsten forms two carbides, monotungsten carbide (WC) and ditungsten carbide (W2C). Tungsten carbide may also exist as a mixture of these two forms with any proportion between the two. Cast carbide is a eutectic mixture of the WC and W2C compounds, and as such the carbon content in cast carbide is sub-stoichiometric, i.e., it has less carbon than the more desirable WC form of tungsten carbide. Cast carbide is prepared by freezing carbide from a molten state and may be subjected to crushing and comminuting to form the resultant particles of the desired particle size.
Macro-crystalline tungsten carbide is essentially stoichiometric WC in the form of single crystals. While most of the macro-crystalline tungsten carbide is in the form of single crystals, some bicrystals of WC are found in larger particles. Macro-crystalline WC is a desirable hardfacing material because of its toughness and stability.
The third type of tungsten carbide used in hardfacing is cemented tungsten carbide, also known as sintered tungsten carbide. Cemented tungsten carbide comprises small particles of tungsten carbide (e.g., 1 to 15 microns) bonded together with a binder metal. Cemented tungsten carbide is made by mixing organic wax, tungsten carbide, typically monotungsten carbide, and cobalt or other iron group metal powders, pressing the mixed powders to form a green compact, and “sintering” the composite at temperatures near the melting point of cobalt. The resulting dense cemented carbide can then be crushed and comminuted to form particles of cemented tungsten carbide for use in hardfacing. Cemented tungsten carbide, such as WC—Co, is well known for its mechanical properties of hardness, toughness and wear resistance, making it a popular material of choice for use in such industrial applications as mining and drilling where its mechanical properties are highly desired. Because of its desired properties, cemented tungsten carbide has been the dominant material used as cutting tools for machining, hardfacing, wear inserts, and cutting inserts in rotary cone rock bits, and substrate bodies for drag bit shear cutters. The mechanical properties associated with cemented tungsten carbide and other cermets, especially the unique combination of hardness, toughness, and wear resistance, make these materials more desirable than either metals or ceramics alone.
Carburized carbide is yet another type of tungsten carbide. Carburized tungsten carbide is a product of the solid-state diffusion of carbon into tungsten metal at high temperatures in a protective atmosphere. Sometimes, it is referred to as fully carburized tungsten carbide. Such carburized tungsten carbide particles usually are multi-crystalline, i.e., they are composed of tungsten carbide agglomerates. Typical carburized tungsten carbide contains a minimum of 99.8% by weight of tungsten carbide, with total carbon content in the range of about 6.08% to about 6.18% by weight.
Regardless of the type of material used, designers continue to seek improved properties (such as improved wear resistance, toughness, thermal resistance, etc.) in all carbide composites.